Reactive spray deposition technology (RSDT) is a method of depositing films or producing nanopowders through combustion of metal-organic compounds dissolved in a solvent. This technology produces powders of controllable size and quality by changing process parameters to control the stoichiometry of the final product. This results in a low-cost, continuous production method suitable for producing a wide range of fuel cell related catalyst films or powders. In this work, the system is modified for direct deposition of both unsupported and carbon supported layers on proton exchange membrane (PEM) fuel cells. The cell performance is investigated for platinum loadings of less than 0.15 mg/cm² using a heterogeneous bi-layer consisting of a layer of unsupported platinum followed by a composite layer of Nafion®, carbon and platinum. Comparison to more traditional composite cathode architectures is made at loadings of 0.12 and 0.05 mg platinum/cm². The composition and phase of the platinum catalyst is confirmed by XPS and XRD analysis while the particle size is analyzed by TEM microscopy. Cell voltages of 0.60 V at 1 A/cm² using H₂/O₂ at a loading of 0.053 mg platinum/cm² have been achieved. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Demand for lithium (Li) and cobalt (Co) is on the rise, due in part to their increased use in rechargeable Li-ion batteries (RLIB). Current recycling processes that utilize chemical leaching efficiently recover in Li and Co from the cathode material in spent batteries; however, these processes are costly and emit hazardous waste into the environment. Therefore, a more sustainable process for recycling Li and Co is needed, and bioleaching may provide a solution. Fungal bioleaching has been shown in previous studies to effectively mobilize metals (Pb, Al, Mn, Cu, and Zn) from mine tailings, electronic scrap, and spent batteries with organic acids. However, little is known regarding fungal tolerance to Li and Co, and if the concentrations of organic acids excreted by fungi can effectively leach Li and Co from the cathode material. In order to address these questions, experiments were first conducted to test the Li and Co leaching efficiency with organic acids at concentrations similar to what has been previously reported in fungal cultures. The remaining experiments were performed with three fungal species: Aspergillus niger, Penicillium chrysogenum, and Penicillium simplicissimum. First, fungal biomass production, pH and organic acid excretion were examined when the fungi were grown in Czapek dox broth (CDB) or Sabouraud dextrose broth (SDB). Second, fungal biomass production and pH were examined when the fungi were grown in the presence of Li or Co. This determines tolerance of the fungi to the metals, and if fungal processes were inhibited by the metals. Third, bioleaching was performed with cathode material from RLIB in batch cultures to test the ability of organic acids excreted by A. niger to mobilize Li and Co. Three bioleaching strategies, one-step, two-step, and spent-medium leaching techniques were used to mobilize Li and Co from the cathode in RLIB. Low concentrations of organic acids similar to what is excreted by fungi have not been tested to leach Li and Co from the cathode in RLIB. Results from chemical leaching with low concentrations of organic acids in this study indicate that organic acid leaching efficiency can be increased by utilizing higher concentrations (above 50 mM) of citric or oxalic acid to mobilize Li or Co from the cathode in RLIB. Furthermore, 100 mM of citric acid or 100 mM of oxalic acid mobilized more Co or Li than mixtures of organic acids. Notably the addition of hydrogen peroxide to mixed concentrations of organic acids significantly improved mobilization of Li and Co under abiotic conditions. Different growth media may alter biomass production and potentially organic acid excretion by the three fungal species. Analysis of biomass production by A. niger and P. simplicissimum showed that differences in media composition between CDB and SDB did not affect collected biomass for each species. However, CDB cultures with P. chrysogenum had significantly less biomass than SDB cultures after 10 days of growth. Differences in growth by P. chrysogenum between CDB and SDB may be attributed to preferred nutrients and/or low pH present in SDB cultures. Biomass production by the three fungi increased up to day 10 in CDB or SDB. This result indicated that nutrients in CDB or SDB were not limiting toward fungal growth. Cultures with A. niger had the highest concentrations of organic acids (50 mM of oxalic acid), followed by cultures with P. simplicissimum (30 mM oxalic acid), and P. chrysogenum (less than 5 mM oxalic acid). Organic acids excreted by all three fungal species were detected in cultures in CDB, while only A. niger and P. chrysogenum excreted organic acids in SDB cultures. Metals such a Li or Co present in the cathode of RLIB may be toxic to fungal processes when exposed to high metal concentrations. Metal tolerance experiments indicate that biomass production by the three fungi was significantly inhibited by 100 mg/L Co compared to controls, which contained no metal. Li at a concentration of 1000 mg/L inhibited biomass production by A. niger and P. simplicissimum. However, biomass production by P. chrysogenum was not significantly inhibited by 1000 mg/L Li. I found that P. simplicissimum was the most susceptible to toxic effects of Li and Co among the three fungi. In A. niger cultures amended with 100 mg/L Li or Co, pH at day 5 was similar to control cultures of A. niger without metals (pH 3.0 – 3.4), whereas pH was significantly higher in cultures with 1000 mg/L of Li or Co (pH 7.1 – 7.3). Cultures of A. niger were exposed to the cathode material from RLIB to test the leaching efficiency of excreted organic acids after mobilizing Li and Co. In bioleaching experiments with A. niger, organic acids excreted in the presence of cathode material from RLIB were quantified at concentrations under 50 mM. At the end of bioleaching experiments with A. niger, 40 mM tartaric acid was detected and was the highest produced organic acid in bioleaching cultures. However, with conditions set in this study, organic acids excreted by A. niger mobilized only ̴7% of Co and 20% of Li when using spent medium with cathode material from RLIB. According to findings in chemical leaching experiments, concentrations of organic acids higher than 50 mM will be required in fungal cultures to increase mobilization of Li or Co from the cathode material in RLIB. Modifying growth media to include higher concentrations of sucrose will potentially increase organic acid excretion as demonstrated in previous publications. Future studies should focus on how to maximize organic acid excretion by fungi when exposed to metals found in the cathode of RLIB.

>Magister Scientiae - MSc / In the wide search for advanced materials for next generation lithium-ion batteries, lithium manganese orthosilicate, Li₂MnSiO₄ is increasingly gaining attention as a potential cathode material by virtue of its ability to facilitate the extraction of two lithium ions per formula unit, resulting in a two-electron redox process involving Mn²⁺/Mn³⁺ and Mn³⁺/Mn⁴⁺ redox couples. This property confers on it, a higher theoretical specific capacity of 333 mAhg⁻¹ which is superior to the conventional layered LiCoO₂ at 274 mAhg⁻¹ and the commercially available olivine LiFePO₄ at 170 mAhg⁻¹. Its iron analogue, Li₂FeSiO₄ has only 166 mAhg⁻¹ capacity as the Fe⁴⁺ oxidation state is difficult to access. However, the capacity of Li₂MnSiO₄ is not fully exploited in practical galvanostatic charge-discharge tests due to the instability of the delithiated material which causes excessive polarization during cycling and its low intrinsic electronic conductivity. By reducing the particle size, the electrochemical performance of this material can be enhanced since it increases the surface contact between the electrode and electrolyte and further reduces the diffusion pathway of lithium ions. In this study, a versatile hydrothermal synthetic pathway was employed to produce nanoparticles of Li₂MnSiO₄, by carefully tuning the reaction temperature and the concentration of the metal precursors. The nanostructured cathode material was further coated with a thin film of aluminium oxide in order to modify its structural and electronic properties. The synthesized materials were characterized by microscopic (HRSEM and HRTEM), spectroscopic (FTIR, XRD, SS-NMR, XPS) and electrochemical techniques (CV, SWV and EIS). Microscopic techniques revealed spherical morphologies with particle sizes in the range of 21-90 nm. Elemental distribution maps obtained from HRSEM for the novel cathode material showed an even distribution of elements which will facilitate the removal/insertion of Li-ions and electrons out/into the cathode material. Spectroscopic results (FTIR) revealed the vibration of the Si-Mn-O linkage, ascertaining the complete insertion of Mn ions into the SiO₄⁴⁻ tetrahedra. XRD and ⁷Li MAS NMR studies confirmed a Pmn21 orthorhombic crystal pattern for the pristine Li₂MnSiO₄ and novel Li₂MnSiO₄/Al₂O₃ which is reported to provide the simplest migratory pathway for Li-ions due to the high symmetrical equivalence of all Li sites in the unit cell, thus leading to high electrochemical reversibility and an enhancement in the overall performance of the cathode materials. The divalent state of manganese present in Li₂Mn²⁺SiO₄ was confirmed by XPS surface analysis. Scan rate studies performed on the novel cathode material showed a quasi-reversible electron transfer process. The novel cathode material demonstrated superior electrochemical performance over the pristine material. Charge/discharge capacity values calculated from the cyclic voltammograms of the novel and pristine cathode materials showed a higher charge and discharge capacity of 209 mAh/g and 107 mAh/g for the novel cathode material compared to 159 mAh/g and 68 mAh/g for the pristine material. The diffusion coefficient was one order of magnitude higher for the novel cathode material (3.06 x10⁻⁶ cm2s⁻¹) than that of the pristine material (6.79 x 10⁻⁷ cm2s⁻¹), with a charge transfer resistance of 1389 Ω and time constant (τ) of 1414.4 s rad⁻¹ for the novel cathode material compared to 1549 Ω and 1584.4 s rad-1 for the pristine material. The higher electrochemical performance of the novel Li₂MnSiO₄/All₂O₃ cathode material over the pristine Li₂MnSiO₄ material can be attributed to the alumina nanoparticle surface coating which considerably reduced the structural instability intrinsic to the pristine Li₂MnSiO₄ cathode material and improved the charge transfer kinetics.

Les micro-plasmas constituent une technologie d'avenir pour des applications aussi nombreuses que diverses : dépollution, traitement de surface, applications bio-médicales, accélération aérodynamique... Nous avons étudié ces micro-plasmas dans des gaz inertes (hélium ou argon), en les alimentant en courant continu dans des structures de type micro-cathode creuse. Afin de comprendre les mécanismes physiques régissant leur comportement, nous les avons caractérisés par plusieurs diagnostics, notamment par caméra ICCD et par spectrométrie d'émission optique. Ce dernier diagnostic nous a permis de déterminer la température du gaz des micro-plasmas, par l’analyse de la structure rovibrationnelle des raies du second système positif de l’azote (présent à l’état de traces), mais aussi d’effectuer des mesures de densité électronique, en analysant l’élargissement Stark de la raie H béta. Ces paramètres physiques obtenus expérimentalement, ont été comparés à leurs équivalents obtenus par simulation (logiciel GdSIM du laboratoire Laplace). Ce travail de thèse a également permis de montrer la possibilité d’atteindre le régime luminescent anormal d’un micro-plasma, en réduisant l’aire de la surface cathodique extérieure de la micro-cathode creuse. Ce régime de fonctionnement s’accompagne d’une hausse rapide de la température du gaz, ainsi que d’un phénomène d’hystérésis qui apparaît sur une courbe I-V, pour une rampe d’alimentation en courant linéairement croissante puis décroissante. Dans le cas de plusieurs micro-plasmas fonctionnant en parallèle, nous avons mis à jour un nouveau mécanisme, expliquant l’allumage des cavités de proche en proche. / The micro-plasmas are a promising technology for a lot of applications: environmental remediation, surface treatment, bio-medical applications, aerodynamic acceleration ... Our micro-plasmas are generated in microhollow cathode (M.H.C) structures, supplied by direct current and studied in rare gases (helium or argon). To understand the physical mechanisms ruling their behaviour, they have been characterized by several diagnostics, especially ICCD camera and optical emission spectroscopy. This last diagnostic has been used to determine the micro-plasma gas tempe rature , by analysing the bands 1.3 and 0.2 (from the second . positive system of nitrogen). but also to measure the electron density by analyzing the Stark broadening of the H beta line. We have also carried out simulations with a fully fluid model to obtain the spatial profiles of the electric field, the charge species densities and the gas temperature. Thus, we have studied the breakdown, the self-pulsing regime and the normal glow regime of our micro-plasmas. We have also demonstrated that a micro-plasma can work in the ab normal glow regime, at the condition to limit the cathode surface of the micro-device. For increasing values of curre nt. this abnormal glow regime is accompanied by a fast increase of the gas temperature. Moreove r, when the micro-plasma is supplied by a linear increasing-decreasing DC voltage ramp, this regime is accompanied by the formation of a hysteresis phenome non. At last, in the case of a micro-devi ce with severa 1micro-ho 1I0wcathodes in parallel, we exp lain how the cathode limitation favours the parallel ignition and is an alternative issue to the individual ballasting.

京都大学 / 0048 / 新制・課程博士 / 博士(人間・環境学) / 甲第22549号 / 人博第952号 / 新制||人||226(附属図書館) / 2019||人博||952(吉田南総合図書館) / 京都大学大学院人間・環境学研究科相関環境学専攻 / (主査)教授 内本 喜晴, 教授 吉田 寿雄, 准教授 戸﨑 充男 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DFAM

This thesis deals with the concept of propulsion for ultralight plane with using fuel cells technology. Here are described the individual kinds of fuel cells and possible fuel. Furthermore it is listed the calculation of low-temperature fuel cell H2 - O2 with polymeric membrane (PEM). The thesis includes also a part with the design drawings of the proposed solutions.

This master´s thesis deals with stability of electrolytes and electrodes using electrochemical methods of Li-ion batteries. The first part of the project is devoted to the characteristics of Li-ion batteries, electrochemical reactions and characteristics of electrode materials. Consenquetial part is concentrated on preparation and measurement of elektrolyte EC : DMC with 1M LiPF6. The elektrolyte was investigated using galvanostatic method, cyclic voltammetry and impedance spectroscopy.

The subject of the master thesis is the extension of the measurement of plasma para- meters by the Langmuir probe in a system with a planar magnetron and a hollow cathode operating in pulse mode. The main tasks are to modify the measuring circuit to increase the maximum probe current and to put the USB oscilloscope into operation for data collection with higher resolution and higher sampling rate. Furthermore, the function of the entire device will be verified using test circuits and also by measuring the probe characteristics in discharges in a system with a magnetron and a hollow cathode in both continuous and pulse mode. 1

Manufacturing of components with complex internal features, e.g. for medical applications, aeronautics or automobile industry, is challenging. Those components are often machined in temporarily and locally separated production stages. As results of these separated stages form deviations and positioning errors increase, which lead to additional efforts for the quality assurance. The technology aimed within the project SwitchECM is expected to allow the machining of different complex features of one workpiece in one single production stage and shall simultaneously allow a high precision. For this purpose, a multi-cathode system will be developed, in which separated cathodes can be switched with specific parameters, depending on the requirements of the pre-defined features. This study will show the capability to machine the workpiece with different parameter sets but the same cathode and device as fundamental work for the machining with a multi-cathode system. Therefore the surface and dissolution characteristics for the material 1.4301 were used to design the process. The machining tasks were determined to deburring and edge shaping. In the experiments, the parameters voltage and working time were selected depending on the final geometry. It will be shown that the deburring task can be handled with nearly no edge shaping and the edge shaping task is suitable to adjust different edge geometries.

Understanding the degradation mechanisms of Li-ion batteries is essential to gain insights into battery aging. The primary research area of this thesis is the positive electrode, NMC811. The purpose of the thesis is to understand how low and elevated temperatures affect the aging of NMC811, by considering the effects on resistance.  The aim of the thesis is to investigate the degradation mechanisms of NMC811. Here, three-electrode Li-ion pouch cells are assembled with LiNi8Mn1Co1O2 (NMC811) as the positive electrode, graphite as the negative, gold wire as the reference electrode, and LiPF6 as the electrolyte. The positive electrode impedance is recorded at temperatures –10, 22, and 40 ºC. Also, symmetric and half cells are built for validation measurements. The Nyquist diagrams are fitted through equivalent circuits to determine the cells’ impedance at voltages 3.8 and 3.0 V vs Li+/Li. The resistances observed and analyzed in this project are the high-frequency resistance, the contact resistance, the charge transfer resistance, and the resistance due to the electrode–electrolyte interphase. By comparing these resistances, it is observed that the charge transfer resistance has the highest dependence on the ambient temperature. The increase in charge transfer resistance at –10 ºC is suggested to depend on the Ni-rich electrode, which tends to contribute to volume changes in the electrode, affecting the intercalation and de-intercalation of Li-ions. The resistance reduces significantly at 40 ºC, due to the loss of lithium inventory in the active material. This thesis has thus shown that temperature has a significant effect on cell internal resistance, especially on the electrode–electrolyte interface, which describes the charge transfer reactions.